Stihl 017

[lefty]

I got this saw. There's another tag on the machine that says 311Y

The owner of this saw couldn't tell me much. It was given to him. It didn't start initially. I cleaned it up and replaced both sides of the carb...diaphragms and gaskets. The carb didn't look bad. Took it all apart and cleaned it.

This is my problem. It will run well for anywhere from 15 seconds to several minutes sometimes. Then during idle, the RPMs will run up, and then it will stall. So it could happen just a few seconds after starting or it could run perfectly for a few minutes and then just start running up and stall. I initially thought it was a venting issue but I checked that and it looks good. It could just run perfectly for a minute or two and then just go all screwy. Air leak maybe?

Thanks
Lefty.

[RoyM]

That is what I am thinking. Can you do a pressure/vacuum test?

[lefty]

I can. I'll do it in the morning and report back. Thank you.

[KE4AVB]

The 017/MS170 chainsaw can be a little picky about the idle mixture and idle speed.

One thing to check is the metering lever height as too low will cause the saw to lean out just like setting it too high will cause it to flood out.

Plus the standard idle mixture setting maybe too lean. The standard setting is one turn out from lightly seated then having the saw idling at 3200 rpm. This is sometimes too lean fuel mixture as it can cause poor acceleration so it must be tune for best acceleration. Also idle speed might be too low even at 3200 rpm so try setting by increasing to where the chain just starts moving and back off approximately 1/4 - 1/2 turn.

And noted it can be vacuum leak so test at .4 bar [5.8 psi] and it should not drop below .03 bar [4.25psi] within 20 seconds. Oil seals tend to fail when subjected to vacuum. On pressure test it is .4 bar holding for 20 seconds. If it fails it can be an oil seal or pan sealing gasket. Don't forget to check the rubber intake manifold.

[lefty]

Thank you. I didn't have a hell of a lot of time today to work on it but I was able to at least squeeze in a leak down. Thanks for the info on that. She's holding the air in both directions so I'm hoping to tackle the carb adjustment tomorrow and see if I can't get this one out of here. If I can't, my guess is I'll be looking at a new carb?

[lefty]

I was pondering my test and was wondering...does it matter where the piston is during the leakdown? Should I turn the crank after charging with air to make sure it makes its way down to the case? Or does it just bleed past the rings quickly and charge the case?

Thanks.

[bgsengine]

Yes, you could rotate the crank to move piston around (very very slowly) but only time you want to note an actual result, you won't want anything moving while monitoring for pressure/vacuum loss. However, it would be worthwhile to watch for loss while rotating crank, as it could still be a bad seal (slight out-of-round or groove or bad spot in crank bearing also) in just one small spot that won't show until crank is in right position... I have found a couple that way, that otherwise would have passed the testing with flying colors (one was a cracked ball bearing race that allowed bearing movement out of round, the other one was a crank that shifted sideways slightly randomly, when it shifted one way, things sealed and it passed, when it shifted the other way (back into the groove the hardened seal lip had worn into crank) it failed. So, I never assume a pressure/vacuum test has passed until I have also moved crank around a bit while monitoring (and actually, have had them continue to pass the entire time I was moving crank around, as long as crank is turned slowly enough, and realizing that you'll see needle flutter while doing so)

[lefty]

Thank you.

[Arkie]

Has symptoms of slight air leak.
How does it act when trying to re-start? (like needs lots of choke and several rope pulls or or no choke and ?????
I sometime throw a clone carb on those just to see, but you have to keep a heads up some of them carbs are slightly different. (close but no cigar) If the clone carb acts ok I then try to repair the OEM carb if it's my own eq. (I do not like to run clone carbs on my Stihls is why)


You can get some 2nd opinions here.

https://www.arboristsite.com/forums/chainsaw.9/

You might want to ask for a parts list or service manual. Sometimes some carb tips are at the very last part of the service manual and or parts list.

You ask about the position of the piston when doing the leak down test. The leak down test on a chainsaw is the crank case leak down (crankcase sealed ok and not leaking), not the piston ring leak down so no the piston can be left in place at first.
If the crankcase is holding 5 lbs of pressure then do as bsengine says, slowly rotate the crank and watch the air pressure, then wiggle rotate the crank back and forth.
Also test the running with the chain off. If the idling gets better with the chain and bar off and gets worse after you install and tension the chain this is a hint that the clutch/chain side seal is leaking. A tip test is also a hint that a crank seal is leaking if you tip the saw sideways or upside down and the idling changes. (the Crank is shifting position and causing the seal to leak or a plastic bearing crankshaft roller cage is broken and the crank is shifting position up/down as it rotates.
If that one has the carb intake boot, check that boot area good.
I would pull the muffler and take a gander at the piston to make sure I'm not working on a dying horse. If piston is scored the saw has be run leaned out (overheated piston) and no need in further testing of other things unless you want to do a major repair. (reason I mention this is I've seen chainsaws check good compression but the piston/cylinder is eating itself due to issues previously and fixing a seal leak or carb is just placing a band aid on cancer. (scored piston and cylinder)

You have found out why someone gave the saw away.

[lefty]

That's actually the first thing I thought of...who would give away a perfectly good saw?

Unfortunately, I was tied up all day so I didn't have a chance to get at it, but will tomorrow. I can verify, at this point, that the piston and cylinder look good. I've viewed them from both the muffler and intake sides. My concern regarding the leak down I did was that there's a chance that the piston may have been close to TDC. In that case, I'm imagining I wasn't testing anything. So I'll go at that tomorrow with your and BG's suggestions. If there is a leak...I'll chase it down.

My setup has been to install the carb over a piece of rubber so the boot is involved in the test. If I start losing pressure, I'll dig deeper and maybe spray some soapy water around the seals. I'm guessing this is carb-related but before I start getting parts, I want to make sure there's no leak.

I always appreciate the detailed explanations as I always learn from them. I'll report back with my findings.